Irreversible Electroporation Parameters Research Articles

Scheduled dosage regimen by irreversible electroporation of loaded erythrocytes for cancer treatment.

Precise control of cargo release is essential but still a great challenge for any drug delivery system. Irreversible electroporation (IRE), utilizing short high-voltage pulsed electric fields to destabilize the biological membrane, has been recently approved as a non-thermal technique for tumor ablation without destroying the integrity of adjacent collagenous structures. Due to the electro-permeating membrane ability, IRE might also have great potential to realize the controlled drug release in response to various input IRE parameters, which were tested in a red blood cell (RBC) model in this work. According to the mathematical simulation model of a round biconcave disc-like cell based on RBC shape and dielectric characteristics, the permeability and the pore density of the RBC membrane were found to quantitatively depend on the pulse parameters. To further provide solid experimental evidence, indocyanine green (ICG) and doxorubicin (DOX) were both loaded inside RBCs (RBC@DOX&ICG) and the drug release rates were found to be tailorable by microsecond pulsed electric field (μsPEF). In addition, μsPEF could effectively modulate the tumor stroma to augment therapy efficacy by increasing micro-vessel density and permeability, softening extracellular matrix, and alleviating tumor hypoxia. Benefiting from these advantages, this IRE-responsive RBC@DOX&ICG achieved a remarkably synergistic anti-cancer effect by the combination of μsPEF and chemotherapy in the tumor-bearing mice model, with the survival time increasing above 90 days without tumor burden. Given that IRE is easily adaptable to different plasma membrane-based vehicles for delivering diverse drugs, this approach could offer a general applicability for cancer treatment.

Electroporation Parameters for Human Cardiomyocyte Ablation In Vitro.

Cardiac ablation with irreversible electroporation (IRE) is quickly being established as a modality of choice for atrial fibrillation treatment. While it has not yet been optimised, IRE has the potential to significantly limit collateral damage and improve cell-specific targeting associated with other energy sources. However, more tissue and cell-specific evidence is required to demonstrate the selective threshold parameters for human cells. The aim here is to determine the optimal ablation threshold parameters related to lesion size for human cardiomyocytes in 2D culture. Conventional biphasic pulses of different field strengths and on-times were delivered in a monolayer culture system of human AC16 cardiomyocytes. The dynamics of cell death and lesion dimensions were examined at different time points. Human cardiomyocytes are susceptible to significant electroporation and cell death at a field strength of 750 V/cm or higher with 100 μs pulses. Increasing the IRE on-time from 3 ms to 60 ms reduces the effective field threshold to 250 V/cm. Using very short pulses of 2 μs and 5 μs also causes significant cell death, but only at fields higher than 1000 V/cm. A longer on-time results in more cell death and induced greater lesion area in 2D models. In addition, different forms of cell death are predicted based on the evolution of cell death over time. This study presents important findings on the ability of different IRE parameters to induce human cardiomyocyte cell death. Lesion size can be tuned by appropriate choice of IRE parameters and cardiomyocytes display an upregulation of delayed cell death 24 h after electroporation, which is an important consideration for clinical practice.

Effect of irreversible electroporation parameters and the presence of a metal stent on the electric field line pattern

The final ablation zone created with irreversible electroporation (IRE) depends on the size, shape and strength of the electric field that is influenced by several parameters. A profound understanding of the effect of IRE parameter alterations on the electric field are a prerequisite for a safe and effective treatment. Here, we demonstrate a semolina in castor oil model that enables visualization of the static electric field developed by a high-voltage generator between two needle-electrodes. We intuitively visualize the variation in electric field line pattern for selected IRE parameters; active needle length, inter-needle distance, applied voltage and presence of a nearby metal stent, by cameras in three dimensions. The observations were compared to and supported by two-dimensional numerical simulations of the electric field. Our semolina model visualizes the disturbance of the electric field by a metal stent, potentially leading to an incomplete tumour ablation between the needles. The reduction in electric field strength and the area at risk for incomplete tumour ablation are confirmed by the numerical simulations. The semolina model provides insight in the fundamental physics of the electric field, the effect of alterations in IRE parameter combinations and presence of a metal stent within the ablation zone.

Irreversible electroporation in the eradication of rabbit VX2 cervical tumors.

The aim of this study was to evaluate the effects of irreversible electroporation (IRE) on the eradication of rabbit VX2 cervical tumors. A VX2 cervical cancer model was first made in 20 New Zealand rabbits. IRE ablation was performed for the cervical cancers of 15 rabbits when the diameter of the tumor was about 1.0-1.5cm. The control group (n=5) did not receive IRE ablation. The gross pathology, ultrasound, computed tomography, hematoxylin and eosin, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, and proliferating cell nuclear antigen immunohistochemical staining were performed to evaluate the efficacy of IRE on cervical cancer. All the rabbits tolerated the IRE ablation without serious complications. The tumors treated by IRE slightly increased in size during the first two days, but decreased gradually. IRE caused tumor cell death efficiently, mainly through cell apoptosis; however, it did not induce complete tumor ablation in our study. The results suggested that IRE could eradicate rabbit VX2 cervical tumors efficiently. However, the optimal IRE parameters remain to be determined.

Mathematical Models Describing Chinese Hamster Ovary Cell Death Due to Electroporation In Vitro.

Electroporation is a phenomenon used in the treatment of tumors by electrochemotherapy, non-thermal ablation with irreversible electroporation, and gene therapy. When treating patients, either predefined or variable electrode geometry is used. Optimal pulse parameters are predetermined for predefined electrode geometry, while they must be calculated for each specific case for variable electrode geometry. The position and number of electrodes are also determined for each patient. It is currently assumed that above a certain experimentally determined value of electric field, all cells are permeabilized/destroyed and under it they are unaffected. In this paper, mathematical models of survival in which the probability of cell death is continuously distributed from 0 to 100 % are proposed and evaluated. Experiments were performed on cell suspensions using electrical parameters similar to standard electrochemotherapy and irreversible electroporation parameters. The proportion of surviving cells was determined using clonogenic assay for assessing the ability of a cell to grow into a colony. Various mathematical models (first-order kinetics, Hülsheger, Peleg-Fermi, Weibull, logistic, adapted Gompertz, Geeraerd) were fitted to experimental data using a non-linear least-squares method. The fit was evaluated by calculating goodness of fit and by observing the trend of values of models' parameters. The most appropriate models of cell survival as a function of treatment time were the adapted Gompertz and the Geeraerd models and, as a function of the electric field, the logistic, adapted Gompertz and Peleg-Fermi models. The next steps to be performed are validation of the most appropriate models on tissues and determination of the models' predictive power.

Three-dimensional analysis of irreversible electroporation: Estimation of thermal and non-thermal damage

Irreversible electroporation (IRE) is a novel method to ablate abnormal cells by applying a high voltage between the electrodes punctured in abnormal tissues. The cell membrane exposed to the potential difference above a certain threshold is permanently disrupted, which consequently induces cell necrosis. One of the advantages of the IRE is that the extracellular matrix (ECM) can be kept intact, which is favorable for healing. Thus, it is important to determine an optimal condition of electric pulses and electrode configuration prior to a clinical application so that a proper volume of the targeted tissue is ablated without thermal damage resulted from the Joule heating. The aims of this study were, therefore, to estimate the possible temperature rise during the IRE by a nondimensional 3-D analysis, and to reveal the risk of ECM denaturation caused by the IRE parameters such as electrode dimension, the distance between two electrodes, and the applied voltage. The heat conduction equation and the Laplace equation in non-dimensional forms were solved numerically using the finite element method for the IRE with a pair of rod-shaped electrodes placed in a simulated tissue. Numerical analysis clarified that concentration of electric current induced local heat generation, which resulted in the formation of hot spots near the base and the tip of electrodes. The highest temperature rise occurred at the base of electrodes adjacent to the insulated surface. The result was significantly different from a two-dimensional (2-D) analysis due to end effects, suggesting that the 3-D analysis is required to determine the optimal condition. The region of ablated tissue and its volume were also shown as a function of IRE parameters. This provides useful information for a preoperative simulation of the IRE. Finally, the accumulation of the thermal damage was estimated for three kinds of tissue, i.e., epidermis, aorta, and skin collagen. Although the IRE usually uses a short electric pulse duration from several ten to hundred microseconds, our study demonstrated that even the short pulses in the order of hundred microseconds have a risk for the thermal denaturation depending on tissues and the pulse magnitude.

2:26 PM Abstract No. 88 - Irreversible electroporation (IRE) in cirrhotic liver: preliminary experience in a large animal model

Purpose To compare the efficacy of tissue ablation using IRE in cirrhotic versus normal liver parenchyma in a porcine model. Materials and Methods Eight pigs received a mixture containing iodized oil and ethanol into the hepatic artery to induce liver injury. Cirrhosis was allowed to develop over 4 weeks. Four control animals received a sham hepatic arterial injection of normal saline. CT-guided IRE lesions were created using paired electrodes (18g, 2 cm tip) and a Nanoknife generator (Angiodynamics, Fremont, CA) in cirrhotic (n=14 lesions) and normal liver (n=8 lesions) with the aid of cardiac gating. All animals were euthanized within three hours of the ablation procedure. IRE parameters and pathological data were recorded and analyzed. Immunohistochemical analysis of cleaved caspase-3 was used to assess for apoptosis. These data were compared and subject to statistical analysis using the Satterthwaite t-test. Results Cirrhosis was successfully induced in all experimental animals with histological analysis revealing a median METAVIR score of 3.38. The median calculated electrical resistance of the liver parenchyma during pulse application was greater in the cirrhotic parenchyma 113.9 ohm [95% CI: (92.2,134.7)] than normal liver 90.2 ohm [95% CI: (53.4,126.9)], but it failed to reach statistical significance (p=0.05). The mean ablation volume in the cirrhotic and normal livers at gross pathology was 17.2 cm3 [95% CI: (14.3,20)] and 11.8 cm3 [95% CI: (9.7,13.8)], respectively. Difference in ablation volumes was also not statistically significant (p=0.48). Histological analysis of ablation lesions was similar in both groups and characterized by hepatocellular dissociation often associated with hemorrhage and sinusoidal dilatation with minimal surrounding inflammation. Hepatocytes did not show any substantial evidence of apoptosis at the time of necropsy. Conclusion IRE tissue destruction appears equally effective in cirrhotic and normal liver parenchyma in a porcine model. Although, a trend toward greater electrical resistance was observed in the cirrhotic liver, it did not impact the overall volume of ablation.

Irreversible Electroporation: An In Vivo Study with Dorsal Skin Fold Chamber

Irreversible electroporation (IRE) has been proposed to destroy large amounts of tumorous tissue and shows advantages over thermal therapies. Unfortunately, carefully constructed studies assessing impact in in vivo tumor systems and a direct comparison of IRE with thermal therapy are lacking. In this study, we investigate the effect of IRE in a human prostate cancer (LNCaP) grown in a thin, essentially two-dimensional, dorsal skin fold chamber system. Detailed experimental characterizations of the electrical and thermal responses of the tissue were performed yielding the first thermal response measurement in vivo of its kind that we are aware of. The interaction and coupling of electrical and thermal responses were further discussed. The threshold of the tumor injury was determined for human prostate tumor model, and the threshold value (600-1300 V cm(-1)) is dependent on the IRE parameters including pulse duration and pulse number. This dependence was explained in the context of tissue electrical conductivity change during IRE. Further, the thermal injury was found not to be a dominant factor in IRE with our system, which is in agreement with previous numerical studies. Finally, it appears that the local electrical heterogeneity of the tumor tissue reduces the effectiveness of IRE in some sections of the tumor (leading to live tumor patches).

Irreversible Electroporation in the Liver: Contrast-enhanced Inversion-Recovery MR Imaging Approaches to Differentiate Reversibly Electroporated Penumbra from Irreversibly Electroporated Ablation Zones

To evaluate the use of contrast material-enhanced magnetic resonance (MR) imaging with conventional T1-weighted gradient-recalled echo (GRE) and inversion-recovery (IR)-prepared GRE methods to quantitatively measure the size of irreversible electroporation (IRE) ablation zones in the liver in a rat model. All studies were approved by the institutional animal care and use committee and were performed in accordance with institutional guidelines. Seventeen adult male Sprague-Dawley rats were divided into four groups. Rats in groups 1-3 (n = 15 total) underwent IRE performed by using different IRE parameters after gadopentetate dimeglumine administration. Rats in group 4 (n = 2) underwent IRE ablation without prior gadopentetate dimeglumine injection to serve as control animals. MR imaging measurements (with conventional T1-weighted GRE and IR-prepared GRE methods) were performed 2 hours after IRE to predict the IRE ablation zones, which were correlated with pathology-confirmed necrosis areas 24 hours after IRE by using the Spearman correlation coefficient. Bland-Altman plots were also generated to investigate the agreement between MR imaging-measured ablation zones and reference standard histologic measurements of corresponding ablation zones. The necrotic areas measured on the pathology images were well correlated with the hyperintense regions measured on T1-weighted GRE images (r = 0.891, P < .001) and normal tissue-nulled IR images (r = 0.874, P < .001); pathology measurements were also well correlated with the smaller hyperintense regions measured on those IR images with inversion times specifically selected to null signal from the peripheral penumbra surrounding the ablation zone (r = 0.939, P < .001). Bland-Altman plots indicated that these penumbra-nulled IR images provided more accurate predictions of IRE ablation zones, with T1-weighted GRE measurements tending to overestimate ablation zone sizes. Contrast-enhanced MR imaging permits accurate depiction of ablated tissue zones after IRE procedures. IR-prepared contrast-enhanced MR imaging can be used to quantitatively measure IRE ablation zones in the liver. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100645/-/DC1.

A Preliminary Study to Delineate Irreversible Electroporation From Thermal Damage Using the Arrhenius Equation

Intense but short electrical fields can increase the permeability of the cell membrane in a process referred to as electroporation. Reversible electroporation has become an important tool in biotechnology and medicine. The various applications of reversible electroporation require cells to survive the procedure, and therefore the occurrence of irreversible electroporation (IRE), following which cells die, is obviously undesirable. However, for the past few years, IRE has begun to emerge as an important minimally invasive nonthermal ablation technique in its own right as a method to treat tumors and arrhythmogenic regions in the heart. IRE had been studied primarily to define the upper limit of electrical parameters that induce reversible electroporation. Thus, the delineation of IRE from thermal damage due to Joule heating has not been thoroughly investigated. The goal of this study was to express the upper bound of IRE (onset of thermal damage) theoretically as a function of physical properties and electrical pulse parameters. Electrical pulses were applied to THP-1 human monocyte cells, and the percentage of irreversibly electroporated (dead) cells in the sample was quantified. We also determined the upper bound of IRE (onset of thermal damage) through a theoretical calculation that takes into account the physical properties of the sample and the electric pulse characteristics. Our experimental results were achieved below the theoretical curve for the onset of thermal damage. These results confirm that the region to induce IRE without thermal damage is substantial. We believe that our new theoretical analysis will allow researchers to optimize IRE parameters without inducing deleterious thermal effects.